1. Field of the Invention
The present invention relates generally to surgical cutting instruments and, more particularly, to surgical cutting instruments having an elongate inner member rotatably disposed within an elongate outer tubular member having a cutting window at a distal end which cooperates with or permits the inner member to cut or abrade bodily tissue.
2. Discussion of the Related Art
Surgical cutting instruments in which an elongate inner member is rotated within an elongate outer tubular member have become well accepted in surgical procedures where access to the surgical site is gained via a narrow portal or passage. Typically, the outer tubular member includes a distal end with an opening for defining a cutting port or window and the inner member includes a distal end with a cutting tip for engaging bodily tissue via the opening. Proximal ends of the inner and outer members are commonly secured to hubs which attach to a handpiece having a motor for rotating the inner member relative to the outer tubular member. The distal end of the inner member can have various configurations dependent upon the surgical procedure to be performed, with the opening in the distal end of the outer tubular member being suitably configured to cooperate with the particular configuration of the distal end of the inner member to cut, resect or abrade tissue. Often the inner member is tubular so that the loose tissue resulting from a cutting, resecting or abrading procedure can be aspirated through the hollow lumen of the inner member.
While most of the aforementioned surgical cutting instruments have a straight, elongate outer tubular member and a straight, elongate inner tubular member concentrically disposed in the outer tubular member, angled configurations have been produced in which respective axes of the distal tips of the inner and outer tubular members are offset or bent at a fixed angle relative to respective axes of the proximal ends of the inner and outer members. Examples of such fixed-angle, rotary tissue cutting instruments are shown in U.S. Pat. No. 4,646,738 to Trott and U.S. Pat. No. 5,152,744 to Kraus et al. Variable-angle rotary tissue cutting instruments, such as that described in U.S. Pat. Nos. 5,411,514 and 5,601,586 to Fucci et al, permit the user to bend the outer tube to a user-selected angle while still enabling the inner tube to be selectively inserted into and removed from the outer tube; however, known fixed-angle and variable-angle rotary tissue cutting instruments typically have a bend with a radius of curvature on the order of about 2 to 4 inches and are typically not capable of being bent beyond 15xc2x0. While the relatively small bend angle and relatively large radius of curvature of these angled tissue cutting instruments is generally suitable for most types of arthroscopic surgery, such instruments are of little use in certain types of head and neck surgery because they are not able to access surgical sites such as the maxillary sinus area which is normally accessed with hand instruments such as ball elevators and suction probes having bend angles of about 40xc2x0 and radii of curvature of the order of 1.5 inches or less. Accordingly, it would be desirable for a rotary tissue cutting instrument to operate over an increased range of bend angles while at the same time reducing the radius of curvature of the bend for use in head and neck surgery.
In straight rotary tissue cutting instruments, the elongate tubular body or shaft of the inner member is generally integrally formed with the cutting tip and the proximal end of the shaft is generally permanently affixed to a plastic hub. In the case of fixed-angle rotary tissue cutting instruments, however, a flexible coupling is generally interposed between the tubular drive shaft and the cutting tip. In U.S. Pat. No. 5,620,415 to Lucy et al, U.S. Pat. No. 5,620,447 to Smith et al and U.S. Pat. No. 5,152,744 to Kraus et al, the flexible coupling is merely a portion of the inner member which is provided with relief apertures formed in the cylindrical surface to enable the inner member to bend as it rotates. In U.S. Pat. No. 5,529,580 to Kusunoki et al, U.S. Pat. No. 4,646,738 to Trott, U.S. Pat. No. 5,437,630 to Daniel et al, and U.S. Pat. Nos. 5,286,253, 5,411,514 and 5,601,506 to Fucci et al, the flexible coupling is formed of a plurality of counter-wound coiled metallic springs bonded to and interposed between the tubular body and the cutting tip.
One disadvantage of known flexible couplings is their inability to transmit sufficient torque at high speeds through angles much greater than 15xc2x0 and bend radii less than 2.0 inches. In the case of flexible couplings in the form of coiled springs, there is also the possibility that gaps will develop between the coils as the coupling bends thereby resulting in a decrease of vacuum through the lumen of the inner member and a diminution of the ability of the instrument to aspirate loose tissue through the lumen. Another disadvantage associated with the use of a coiled springs as flexible couplings is the tendency of such members to require tightening or preloading when torque is applied before they are capable of transmitting the torque to the cutting tip. Also, coiled metallic springs have a tendency under certain loading conditions to relax or unwind, and thus expand, thereby increasing the possibility of the inner member binding within the outer member.
Accordingly, it is a primary object of the subject invention to overcome the abovementioned disadvantages of the prior art and to improve angled rotary tissue cutting instruments by providing a rotary tissue cutting instrument capable of operating over an increased range of bend angles while at the same time reducing the radius of curvature of the bend for use in head and neck surgery and other parts of the body.
The present invention is generally characterized in an angled rotary tissue cutting instrument including an outer blade assembly, having a rigid tubular member with proximal and distal portions connected by a bend, and an inner blade assembly rotatably disposed within the outer blade assembly and having a tubular drive shaft at a proximal end, a cutting tip at a distal end, and a flexible coupling disposed between the drive shaft and the cutting tip. The drive shaft and cutting tip include neck portions which are disposed telescopically within proximal and distal ends of the coupling. The flexible coupling includes a tubular member formed of a flexible polymeric material, and each of the neck portions includes a lateral opening defining a predetermined flow path for the polymeric material during fabrication so that the flexible polymeric coupling includes inwardly extending portions molded in the place within the openings in the neck portions of the drive shaft and the cutting tip to form permanent, interlocking mechanical joints therewith capable of receiving and transmitting torque. In one embodiment, a pair of bands formed of shrink wrap tubing are disposed around the flexible polymeric coupling adjacent respective proximal and distal ends of the coupling to provide compression directing the flow of polymeric material into the openings in the neck portions during fabrication and to provide a pair of lubricious bearing surfaces at opposite ends of the bend during operation. The flexible coupling can also include a plurality of wires embedded within the polymeric tubular member as reinforcement, the wires preferably being arranged in a plurality of layers wound in opposite directions of angles of about 45xc2x0 relative to the longitudinal axis of the coupling to define a mesh-like structure within the polymeric coupling capable of transmitting torsional forces regardless of the direction of rotation while at the same time being unable to support compressive forces. Using a polymeric coupling in the above manner permits the distal portion of the outer blade assembly to be oriented at angles greater than 30xc2x0 relative to the longitudinal axis of the proximal portion and the distal direction with bend radii equal to or less than 1.5 inches.
Another aspect of the present invention is generally characterized in a method of fabricating an angled rotary tissue cutting instrument including the steps of positioning a neck portion at the proximal end of a cutting tip in the distal end of a flexible polymeric coupling of tubular configuration, positioning a neck portion at the distal end of a drive shaft in the proximal end of the flexible polymeric coupling, placing a first band of shrink tubing over a proximal end of the flexible polymeric coupling, placing a second band of shrink tubing over a distal end of the flexible polymeric coupling, heating the shrink tubing and the flexible polymeric coupling to cause the polymeric coupling to flow and the shrink tubing to contract around the polymeric coupling such that the polymeric material flows along predetermined flow paths defined by lateral openings in the neck portions of the drive shaft and cutting tip, and cooling the shrink tubing and the flexible polymeric coupling so that flowed portions of the polymeric coupling harden within the openings in the neck portions to form permanent, interlocking mechanical joints therewith capable of receiving and transmitting torque as an integral blade assembly.
Some of the advantages of the present invention over the prior art are that permanent, interlocking joints can be formed between a flexible coupling and other rotating components of an inner blade member in a rotary cutting instrument without the use of adhesives or pins, that a wider range of manufacturing tolerances and clearances can be accommodated when forming such joints, that torsional forces can be more efficiently transmitted while allowing the coupling to bend, that preloading of the coupling is not required to transmit torsional forces, and that fluid leakage through the inner blade member is minimized.
Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference numerals or by reference numerals having the same last two digits.